Crystal structure and thermochemical properties of bis(1-octylammonium) tetrachlorochromate phase change materials

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A new crystalline complex (C8H17NH3)2CdCl4(s) (abbreviated as C8Cd(s)) is synthesized by liquid phase reaction. The crystal structure and composition of the complex are determined by single crystal X-ray diffraction, chemical analysis, and elementary analysis. It is triclinic, the space group is P−1 and Z = 2. The lattice potential energy of the title complex is calculated to be UPOT (C8Cd(s))=978.83 kJ·mol−1 from crystallographic data. Low-temperature heat capacities of the complex are measured by using a precision automatic adiabatic calorimeter over a temperature range from 78 K to 384 K. The temperature, molar enthalpy, and entropy of the phase transition for the complex are determined to be 307.3±0.15 K, 10.15±0.23 kJ·mol−1, and 33.05±0.78 J·K−1·mol−1 respectively for the endothermic peak. Two polynomial equations of the heat capacities each as a function of temperature are fitted by using the least-square method. Smoothed heat capacity and thermodynamic functions of the complex are calculated based on the fitted polynomials.